The objectives of the proposed research are to explore the sensory and developmental influences on maternal behavior in rats. A knowledge of the stimuli which regualte the expression of a given behavior is essential to a full understanding of that behavior. Further, since a major difference between postpartum and pup-induced maternal behavior is the rapidity with which maternal behavior is diplayed in the former compared to the latter, it is likely that one of the ways in wich hormones act to bring about this short-latency response to change the mother's perception of, or preference for, the stimuli associated with pups. The influence of various aspects of the rat pup stimulus comply (contact: tactile, thermal, taste; exteroceptive: sight, sound, smell on the induction (in virgins), initiation and maintenance (postpartum) of maternal behavior will be assessed by altering the available pup stimuli. The sensory regulation of prolactin secretion in lactating, the lectomized (nipple-removed) postpartum, and virgin mothers will also be assessed. Finally, an elucidation of both the faclitatory and inhibitory mechanisms regulating the expression of maternal behavior may be gained by a developmental analysis. Specificially, experimental, social, and maturational influences on maternal responsiveness will be studied.